buying a mppt vs adding a 100w panel

wild01 · June 2008

hey I will need to upgrade my system soon, I just purchased about 400 more watts of panels bringing the total up to 700 watts, b/c of non matched panels (3 100w 2 50w 1 46w 2 35w 20 5w) I will still be running 12(18)volts from the panels. so here is the question has anyone compared advantages of using mppt controllers vs cost on a small system like mine?

if mppt gets 10-30% more power from my panels then if I added 1 @$600+
10% of 700=70 30%=210 is it 30% more efficient in full sun(b/c that would be a nice payoff, or is it 30% more efficient in shady applications b/c 30% of nothing is still nothing.

I could buy a pwm controller for about $100 and a 125w panel. for the same $600

just thinkin here charge controllers w moving parts would seemingly not be as durably as a panel, has anybody crunched these #'s is there something else I should be considering?

sys info 700 ah 12 volt deka forklift battery xantrex prosine 2.5 currently a 10 amp l-cheapo charge controller. off grid 7500w gas generac in sunny southern colorado. (yes I know my ip address is in portland, I travel a lot for work[millwright])

icarus · June 2008

Re: buying a mppt vs adding a 100w panel

From my experiance, I get about 15% better harvest on average with the mppt. This is very much dependent on battery state of charge and temp. The colder it is the better given equal sun. I tend to keep my batteries very well charged so that they don't benefit as much as if I dropped them further.

An additional advantage of the MPPT is that you could wire your panels together better. I will leave it to those with more experiance with mixed panels to suggest the best way to wire them.

In my mind, if you need a new controller anyway, you should go with a GOOD MPPT. (See posts about BZ products!)

Good luck,

Icarus

System2 · June 2008

Re: buying a mppt vs adding a 100w panel

I wouldn't even consider anything less than an MX-60. Been there, done that, finally got an MX-60 and now see I wasted a lot of money before that. A GOOD MPPT controller does cost a bit more money, but in the end, you're much further ahead. I know that now.
Now, especially in winter when it's needed most, I see a big boost, like 15% on many days.
As for "moving parts" since it was installed last October, I've ever only once seen the fan running on the MX, and even then only when the MX was pumping out over 40 amps on a warm day, and only for short times. Never ran once all winter, even when outputting (with snow reflections and edge of cloud effect) 63 amps! I do expect to see it run more in hot weather, but averaged over a year, it would get little run time, so I'm not worried about that at all.
Wayne

System2 · June 2008

Re: buying a mppt vs adding a 100w panel

wild01 wrote: »

hey I will need to upgrade my system soon, I just purchased about 400 more watts of panels bringing the total up to 700 watts,....

You're about to do an upgrade, I guess it's because you see value in solar power. To me, that says that you'll upgrade again. Go for the MX-60 or better. I battled with the same question when I bought mine four or five years ago. I never regretted paying the extra bux for it, especially when you consider the flexibility of array voltage vs. battery voltage and the ability to run higher gauge (thinner) wire from the array to the controller without voltage drop. I went from 24 volt UPS to 48 volt Outback GTFX 3048 and only had to reconfigure my battery and array wiring.

Cheers,

Bad Apple

Brock · June 2008

Re: buying a mppt vs adding a 100w panel

I will third the MX-60. I think it was the best single improvement in our system. Better for the batteries, easier to use and reliable. I got our about 4 years ago and would recommend it to anyone.

buying a mppt vs adding a 100w panel

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